Ok, thank you! I'll probably just keep it simple and not try to install yaboot over grub but, should I ever attempt it and succeed, I'll be sure to let you know.Hi, nice that you would like to try this guide. As you correctly pointed out, Debian now installs Grub as bootloader instead of yaboot. The problem is, that Grub cannot boot your Leopard partition. You either have to boot Leopard using the alt key, which shows you the option to boot OSX, or to manually install yaboot over grub. In the latter case you can choose OSX or Linux from yaboot.
If you are going to try to install yaboot over grub, and you succeed, please tell me how you did it. I will add it to that guide then.